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Rekayasa Trafik, Sukiswo3 Erlang B  Erlang B is a formula for blocking no retrial sources  The Erlang B distribution is used for dimensioning trunk routes. It is based on the following assumptions: –There are an infinite number of sources; –Calls arrive at random; –Calls are served in order of arrival; –Blocked calls are lost; and –Holding times are exponentially distributed.

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Rekayasa Trafik, Sukiswo4 Erlang B  Erlang B is a formula for blocking no retrial sources  The Erlang B distribution is used for dimensioning trunk routes.  It is based on the following assumptions: –There are an infinite number of sources; –Calls arrive at random; –Calls are served in order of arrival; –Blocked calls are lost; and –Holding times are exponentially distributed.

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Rekayasa Trafik, Sukiswo6 Erlang B Example  I am planning a remote PABX connected by a tieline that will be used for all inbound calls to that PABX which will have 780 active ends. I estimate 30mE of inbound traffic per active end, and GOS should be better than  How many trunks do I need in the tie line route?

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Rekayasa Trafik, Sukiswo7 Extended Erlang B  Extended Erlang B is a formula for blocking retrial sources.  A traffic engineering model that, like Erlang B, assumes that an offered call is cleared immediately, with no queuing.  However, Extended Erlang B assumes that the caller encountering blockage (e.g., busy signal or no dial tone) will hang up and immediately attempt the call again, with no overflowing of calls to more expensive routes.  EEB was developed by Jim Jewitt and Jaqueline Shrago of Telco Research  ERL-B:Probability of blocking by Erlang B ERL-B(a,n)  a:Traffic  n:Lines

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Rekayasa Trafik, Sukiswo11 Erlang C  The Erlang C distribution is used for dimensioning server pools where requests for service wait on a first in, first out (FIFO) queue until an idle server is available.  The Erlang C formula is used to predict the probability that a call will be delayed, and can be used to predict the probability that a call will be delayed more than a certain time

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Rekayasa Trafik, Sukiswo12 Erlang C  It is based on the following assumptions: –There are an infinite number of sources; –Calls arrive at random; –Calls are served in order of arrival; –Blocked calls are delayed; and –Holding times are exponentially distributed.

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Rekayasa Trafik, Sukiswo13 Erlang C where: P(>0)=Probability of delay greater than zero N=Number of servers in full availability group A=Traffic offered to group in Erlangs